Technical Field.
This Patent Disclosure relates generally to oscillators, such local oscillators for use in direct conversion RF transmit/receive.
Related Art
Wireless direct conversion architecture use direct RF upconversion (TX signal chain) and/or downconversion (RX signal chain), eliminating conversion at an intermediate frequency (IF). Direct conversion architectures encompass zero and low IF designs, both commonly referred to as zero IF.
Direct conversion (zero IF) architectures commonly use quadrature (IQ) signal conversion (modulation/demodulation), and digital filtering. FIG. 1 functionally illustrates a direct conversion transceiver 10 including I and Q signal paths. For the TX signal path, a digital baseband (BB) signal is input to I and Q signal chains, and converted by DACs 12/14 to analog, and then upconverted to RF by IQ mixers 16/18. The IQ mixers 16/18 are driven by a local oscillator (LO) 20.
Quadrature mismatch/imbalance between the I and Q signal chains generates image signal energy in an image sideband reflected about the LO frequency. The undesired image (sideband) signal energy can appear in frequency bands outside the channel reserved for the TX signal. IQ mismatch can be errors in amplitude, phase and delay.
While this Background information references a direct conversion RF transceiver system, this Patent Disclosure is more generally directed to oscillator design.